Which of the following is correct ?

Options

A. All alkali earth metal salts impart a characteristic colour to Bunsen flame.
B. `CsOH` is most soluble hydroxide among `LiOh, KOH, RbOH` and `CsOH`.
C. Amoung the alkali metals `Li` is most reactive under all the conditions.
D. The reducing character of the alkali metal hydrides following order:
`LiH gt NaH gt KH gt RbH gt CsH`

Explanation

To solve the question regarding which statement about alkali metals is correct, we will analyze each of the provided statements step by step.

### Step 1: Analyze the first statement
**Statement 1:** All alkali metals impart characteristic color to the Bunsen flame.

- **Explanation:** Alkali metals do indeed impart characteristic colors when heated in a flame. This occurs due to the excitation of electrons in the metal atoms, which then emit energy in the form of light when they return to their ground state.
- **Colors produced:**
- Lithium (Li) - Crimson red
- Sodium (Na) - Yellow
- Potassium (K) - Violet
- Rubidium (Rb) - Lilac red
- Cesium (Cs) - Red, violet, and blue

**Conclusion:** This statement is **true**.

### Step 2: Analyze the second statement
**Statement 2:** Cesium hydroxide is most soluble among the hydroxides of the given series.

- **Explanation:** While cesium hydroxide is soluble, it is important to consider the hydration enthalpy. Lithium hydroxide has a higher hydration enthalpy due to the small size of the lithium ion, leading to greater solubility compared to cesium hydroxide.

**Conclusion:** This statement is **false**.

### Step 3: Analyze the third statement
**Statement 3:** Among the alkali metals, lithium is the most reactive.

- **Explanation:** Reactivity in alkali metals increases down the group due to decreasing ionization energy. Lithium has the highest ionization energy among the alkali metals, making it the least reactive. Cesium, having the lowest ionization energy, is the most reactive.

**Conclusion:** This statement is **false**.

### Step 4: Analyze the fourth statement
**Statement 4:** The reducing character of alkali metal hydrides is as follows: LiH < NaH < KH < RbH < CsH.

- **Explanation:** The reducing power of alkali metal hydrides increases as we move down the group. Lithium hydride (LiH) is the least reducing agent due to its thermal stability, while cesium hydride (CsH) is the most reducing agent due to its instability and tendency to release hydrogen.

**Conclusion:** This statement is **false**.

### Final Conclusion:
After analyzing all statements, only **Statement 1** is correct. Therefore, the correct answer is:

**Option A** is the right choice.

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